Battle-scarred champion Sun Yang was attacked over his doping record Saturday as Britain’s Adam Peaty set the first world record of the Rio Olympic swimming competition.

After Sun had cruised into the final of the men’s 400 freestyle, two of his rivals took a swipe at the hulking Chinese over a previous failed drugs test.

Sun has endured a turbulent four years since his breakout victory in London and the sniping began barely moments after the swimmers had toweled down.

Asked about known doping violators Sun and South Korean Park Tae-Hwan competing in Rio, Australian Mack Horton sniffed: “I don’t have time or respect for drug cheats.”

Among Sun’s lengthy rap sheet over the past four years was a three-month doping suspension served secretly in 2014 for taking a banned stimulant, which he said was for a heart complaint.

Canada’s Ryan Cochrane pulled no punches after missing the final.

“I wish it was even across the board,” he fumed. “For an athlete that’s clean it’s really frustrating. Once the Games are over, we’ll all look back and wish this was handled better.”

Roared on by a raucous Brazilian crowd, Peaty smashed his own mark in the men’s 100m breaststroke with a time of 57.55 seconds and looks odds-on to become Britain’s first male Olympic swimming champion since 1988.

“Going down the first 50 I knew it was fast,” he said. “It wasn’t until 25 meters to go the crowd started going ‘Rar!’ I thought there’s no Brazilians in this race, they’ve got to be shouting for something.”

Hungary’s “Iron Lady” Katinka Hosszu just missed a world best in the women’s 400m individual medley, becoming only the second woman to break 4:29 as she clocked a European record 4:28.58 seconds.

In the men’s medley, Japanese gold medal favourite Kosuke Hagino kept plenty in the tank with an easy swim.

Despite some patchy form coming into the Games, Sun turned on the power over the final 100 metres to win his heat in 3:44.23.

American Conor Dwyer clocked the quickest time of 3:43.42 in the final heat, edging out Horton (3:43.84), while former champion Park failed to reach the final on his return from an 18-month steroid ban.

Hagino, who took bronze behind gold medallist Ryan Lochte in 400m medley in London, clocked 4:10.00 as he bids to become the first non-American winner since Hungary’s Tamas Darnyi at the 1992 Barcelona Games.

“I wasn’t going full pelt,” said Hagino. “It was pretty easy — oops, maybe I shouldn’t say that!”

With neither Phelps and Lochte contesting the event, American Chase Kalisz topped the times in 4:08.12, ahead of Japan’s Daiya Seto (4:08.47).

“I didn’t expect to go anywhere near that,” said Kalisz. “I was shocked after I turned around.”

World champion Hosszu looks poised to break the world record held by China’s Ye Shiwen after coming within 0.15 seconds of it, going more than four seconds quicker than Spain’s Mireia Belmonte.

Propelled by the dynamic sister act of Bronte and Cate Campbell, defending champions Australian flexed their muscles in preparation for a tilt at their own world record later Saturday, qualifying in 3:32.39 — over a second faster than an American team featuring Katie Ledecky.

In the women’s 100m butterfly, Syrian teenager Yusra Mardini, who braved a Mediterranean crossing in a leaky dinghy and is representing the first-ever refugee team in Rio, won her heat in 1:09.21.

Sweden’s world record holder Sarah Sjostrom qualified fastest in 56.26 ahead of defending champion Dana Vollmer, the American touching in 56.56 with Canadian schoolgirl Penny Oleksiak third in 56.73. DM

Photo:  Adam Peaty (L) of Great Britain on his way to a new World Record in the men’s 100m Breaststroke Heats of the Rio 2016 Olympic Games Swimming events at Olympic Aquatics Stadium at the Olympic Park in Rio de Janeiro, Brazil, 06 August 2016. EPA/PATRICK B. KRAEMER